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Among the many techniques used to remove toxic dyes from the environment, layered double hydroxides (LDH) are considered to be especially environmentally friendly, but, this quality may be altered by variations in the octahedral Mg/Al molar ratios in the LDH structure. The aim of the present study was to synthesize environmentally sound LDH for use as an economically viable sorbent for the adsorption of reactive brilliant orange X-GN. Layered double hydroxides with Mg/Al molar ratios of 2:1 and 4:1 were prepared by co-precipitation. The materials obtained were characterized by powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, X-ray fluorescence spectroscopy (XRF), and surface-area analysis. Batch experiments were carried out to investigate the effects of contact time, pH, adsorbent dosage, and initial dye concentration on the adsorption behavior of the reactive brilliant orange X-GN by Mg-Al LDH. The results showed that the optimum pH value for dye adsorption was 3.0, at which the adsorption capacities of the reactive brilliant orange X-GN by the 2:1 LDH and the 4:1 LDH at 298 K were 79.370 mg/g and 83.343 mg/g, respectively. Further analysis of the dye-adsorption kinetics show that they fit the pseudo second-order model well. The adsorption equilibrium data showed that the Langmuir model provided better correlation of the equilibrium data than the Freundlich model. This result indicates that LDH provide specific homogeneous sites where monolayer dye adsorption occurs. The results of XRD and FTIR analyses of LDH before and after the dye adsorption demonstrated that the adsorption mechanisms were ion exchange and coulombic attraction.
Multilayer dielectric gratings (MLDGs) are crucial for pulse compression in picosecond–petawatt laser systems. Bulged nodular defects, embedded in coating stacks during multilayer deposition, influence the lithographic process and performance of the final MLDG products. In this study, the integration of nanosecond laser conditioning (NLC) into different manufacturing stages of MLDGs was proposed for the first time on multilayer dielectric films (MLDFs) and final grating products to improve laser-induced damage performance. The results suggest that the remaining nodular ejection pits introduced by the two protocols exhibit a high nanosecond laser damage resistance, which remains stable when the irradiated laser fluence is more than twice the nanosecond-laser-induced damage threshold (nanosecond-LIDT) of the unconditioned MLDGs. Furthermore, the picosecond-LIDT of the nodular ejection pit conditioned on the MLDFs was approximately 40% higher than that of the nodular defects, and the loss of the grating structure surrounding the nodular defects was avoided. Therefore, NLC is an effective strategy for improving the laser damage resistance of MLDGs.
Multilayer dielectric gratings typically remove multiple-grating pillars after picosecond laser irradiation; however, the dynamic formation process of the removal is still unclear. In this study, the damage morphologies of multilayer dielectric gratings induced by an 8.6-ps laser pulse were closely examined. The damage included the removal of a single grating pillar and consecutive adjacent grating pillars and did not involve the destruction of the internal high-reflection mirror structure. Comparative analysis of the two damage morphological characteristics indicated the removal of adjacent pillars was related to an impact process caused by the eruption of localized materials from the left-hand pillar, exerting impact pressure on its adjacent pillars and eventually resulting in multiple pillar removal. A finite-element strain model was used to calculate the stress distribution of the grating after impact. According to the electric field distribution, the eruptive pressure of the dielectric materials after ionization was also simulated. The results suggest that the eruptive pressure resulted in a stress concentration at the root of the adjacent pillar that was sufficient to cause damage, corresponding to the experimental removal of the adjacent pillar from the root. This study provides further understanding of the laser-induced damage behavior of grating pillars and some insights into reducing the undesirable damage process for practical applications.
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